Spot luminaries, such as stage lighting instruments, nightclub lighting instruments and the like having motorized subsystems operated by remote-control means are commonly referred to as “moving lights” or “automated luminaires.” Among these are two general varieties: spot luminaires and wash luminaires. Spot luminaires are similar to the “profile spot” or ellipsoidal reflector spotlight commonly used in theaters, and provide a hard-edged beam of light. This kind of spotlight has a gate or aperture at which various devices can be placed to define the shape or profile of the light beam and has a projection optical system including one or more objective lens elements. A spot luminaire projects an image of the brightly-illuminated gate aperture, including whatever light-shaping, pattern-generating, or image-forming devices might be placed there. Wash luminaires are similar to the “Fresnel Spot” luminaire, which provides a soft-edged, ill-defined beam that can be varied in size by moving the lamp and reflector towards or away from the lens. This kind of wash light has no gate aperture and projects no image, but projects only a soft-edged pool of light shaped by whatever lens or lenses are mounted over the exit aperture of the luminaire.
The development of a spot luminaire having a fully cross-fadeable color mixing system and that is capable of projecting a smooth and uniformly colored beam of light has long been a goal of many lighting manufactures. Although many efforts have been made to develop such luminaires, each of these efforts has failed to achieve the desired goals. A more detailed description of such efforts can be found in U.S. Pat. No. 6,578,987 to Hough et al. which is hereby expressly incorporated by reference.
Typical prior art spot luminaires, and some particular problems associated with them are now discussed with reference to FIGS. 1-6. When referencing the attached figures, like numerals are used to describe like structures when appropriate.
Turning first to FIG. 1, a typical prior art spot luminaire projection optical system is generally indicated by the numeral 10. The optical system 10 includes a lamp 15 and a concave reflector 17. Together the lamp 15 and concave reflector 17 comprise a light source 20. The optical system 10 also includes a field stop/projection gate 25, a light pattern generator 26, and a projection lens 30. The light exits the projection lens 30 and travels over a distance 32 to a distant projection surface 35. For simplicity, the distant projection surface 35 can be considered to be at least six meters (twenty feet) from the projection lens 30. It should be noted that the outer “zigzag” boundary lines between the reflector and lens of this figure represent “edge rays,” which show the outer boundaries of the path of the light from the light source 20 as it travels through the optical system from left to right. This convention applies to all figures incorporated herein. Of course, a single ray of light travels in a straight line unless being reflected or refracting through a lens.
As shown in FIG. 1, the light source 20 can be thought of as illuminating an object 38 (here shown as an up-right arrow) located at the projection gate 25. The object 38 can simply be an aperture formed in the field stop/projection gate 25, or the object 38 can be a light pattern generator 26 which is located at the projection gate 25. An image of the projection gate 25 (or the light pattern generator 26 contained therein) is projected onto the distant projection surface 35. The image of the object 38 is shown by an inverted arrow 40 located on the distant projection surface 35.
The basic optical system which is shown in FIG. 1 will project a polychromatic (white) beam of light. While a white beam of light is useful in many cases, the development of a smooth and uniformly colored beam of light has long been a goal of many lighting manufactures. One of the easiest ways to impart color to a beam of light is through the use of simple absorptive color filters as described below.
Turning now to FIG. 2, the use of absorptive color filters, or “gels”, to impart color to a beam of light is described. Here a typical prior art spot luminaire projection optical system is indicated by the numeral 50. The basic structure of the spot luminaire projection optical system 50 is the same as the optical system 10 described above with reference to FIG. 1. However, in addition to the previously described structures, the optical system 50 also includes an absorptive color filter medium or gel 55 which is shown to the right of the projection lens 30. Since the gel 55 is larger then the projection lens 30, the light exiting the spot luminaire 50 passes through the gel 55. The result is a uniformly colored image 40 of the projection gate 25 and the light pattern generator 26 contained therein.
Referring now to FIG. 3, the use of dichroic filters to impart color to a beam of light is described. Here a typical prior art spot luminaire projection optical system is indicated by the numeral 60. The basic structure of the spot luminaire projection optical system 60 is the same as the optical system 10 described above with reference to FIG. 1. However, in addition to the previously described structures, the optical system 60 also includes a dichroic filter 65. The dichroic filter 65 is typically positioned near the projection gate 25, and can therefore be much smaller than corresponding gel filters of the same color. Due to their small size, it is possible for a number of dichroic filters 65 to be positioned on a wheel hub and rotated into the beam of light, allowing for rapid color changes. All of the light exiting the spot luminaire 60 passes through the dichroic filter 65, resulting in a uniformly colored image 40 of the projection gate 25 and any light pattern generator 26 contained therein.
Turning now to FIG. 4, a variable density patterned dichroic color filter wheel 70 is described. Variable density patterned dichroic color filter wheels 70 such as this have been employed in some prior art spot luminaire projection optical systems. When a color filter wheel 70 is used, it will typically be positioned between the concave reflector 17 and the projection gate 25 (as shown in FIG. 5). As shown best in FIG. 4, the density of the pattern etched onto the color filter wheel 70 varies radially around the wheel 70. FIG. 4 shows the beam of light 75 passing through the color filter wheel 70 as a circle. When the variable density patterned dichroic color filter wheel 70 is rotated, the saturation level of the beam's color will increase or decrease, depending on the position of the wheel 70 in relation to the beam 75.
As best shown by FIG. 4, the patterned dichroic color filter wheel 70 is patterned with a number of fingers 77. The thickness of each finger 77 varies radially around the wheel 70. The saturation of the color in the projected beam 75 depends on the wheel's location in relation to the beam 75. For example, when the wheel 70 is positioned so that the beam of light 75 passes through the clear portion of the wheel 70 (as shown in FIG. 4) the projected beam will be white.
Turning now to FIG. 5, a prior art spot luminaire projection optical system 80 which incorporates a single patterned dichroic color filter wheel 70 is shown. The basic structure of the spot luminaire projection optical system 80 is similar to the optical system described above with reference to FIG. 1. However, in addition to the previously described structures, the optical system 80 also includes a single patterned dichroic color filter wheel 70. The patterned dichroic filter wheel 70 is positioned near the projection gate 25 to ensure that the wheel 70 is as small as possible. Since the pattern 77 is located adjacent to the light pattern generator 26 and the projection gate 25, the pattern 77 etched onto the color filter wheel 70 is visible in the projected beam of light, and will be imaged on the distant projection surface 35. The visibility and imaging of the pattern 77 is undesirable as the projected beam of light will not be smooth and uniformly colored.
In an attempt to ameliorate this problem, a diffusing optical element 85 (FIG. 6) can be placed in the beam path. The diffusing optical element 85 can be positioned between the patterned color filter media 70 and the projection gate 25. The diffusing optical element 85 serves to blur the image of the pattern 77 etched onto the color filter wheel 70. The effect is similar to viewing a scene through a frosted glass window; the detail (in this case the pattern 77 etched onto the color filter 70) is not discernable.
FIG. 6 shows a prior art spot luminaire projection optical system 90. The basic structure of the spot luminaire projection optical system 90 is similar to that of optical system 10 which was described above with reference to FIG. 1. However, in addition to the previously described structures, the optical system 90 also includes a patterned color and dimming apparatus 95 (consisting of cyan, yellow, and magenta color wheels and a patterned dimmer wheel) and a diffusing optical element 85. Although the beam of light will be uniformly colored, the diffusing optical element 85 will scatter light out of the projection lens system 30. This results in a loss of energy in the projected beam, which is undesirable. The light rays being scattered outside of the projection lens 30 are indicated by the numeral 97.
The present invention was principally motivated by a desire to address the above-identified issues. However, the invention is in no way so limited, and is only to be limited by the accompanying claims as literally worded and appropriately interpreted in accordance with the Doctrine of Equivalents.